Electronic device including a protection circuit for a light-emitting device

ABSTRACT

An electronic device is provided that includes a protection circuit for a light-emitting device. The protection circuit comprises a first node adapted to be coupled to an anode of the light-emitting device and a second node adapted to be coupled to a cathode of the light-emitting device. A voltage detection stage is coupled between the first and second nodes. The voltage detection stage is adapted to detect an overvoltage condition between the first and second nodes. Furthermore, the protection circuit comprises a thyristor coupled with its anode to the first node, its cathode to the second node to the voltage detection stage. When the overvoltage condition is detected in normal operation the thyristor is controlled to open so that the current can flow through the thyristor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from German Patent ApplicationNo. 10 2008 031 029.8, filed 30 Jun. 2008, and from U.S. ProvisionalPatent Application No. 61/141,438, filed 30 Dec. 2008, the entireties ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to an electronic device including aprotection circuit for a light-emitting device.

BACKGROUND

In many applications, light-emitting devices, for example light-emittingdiodes (LEDs), are driven in a string; i.e., so that many LEDs areconnected in series with each other. However, if one LED in theseries-connected string of LEDs should fail, this can create an opencircuit condition in which the whole LED string will then be out ofoperation. Time is then lost while the failed LED is detected andrepaired. This is extremely inconvenient and can be dangerous when theLED string is used in applications where safety is an issue, forexample, in street lighting or emergency lighting, etc. In highbrightness LEDs, which are often used in these applications like streetlighting, solid state lighting and emergency lighting, for example,which are intended to have low maintenance costs and a long lifetime,this situation is extremely undesirable. Other applications that areless critical, but where LED failure has an impact, are LED backlightsfor liquid crystal display (LCD) televisions and monitors, which aremoving away from cold cathode fluorescent lamp (CCFL) backlights to LEDbacklights.

LEDs can be subject to failure due to an electrostatic discharge (ESD),which leads to an overvoltage condition. Operating outside its normal orambient voltage range then causes damage to the LED. Solutions forprotecting LEDs from ESD exist, which use a single diode connected in ananti-parallel configuration to the LED within the same package. This cangive the LED protection against electrostatic discharges of up to 2 kV.However, although this solution offers protection to the LED in theevent of an ESD, it does not prevent the loss of operation of a wholestring of LEDs in the case of failure of just one LED in the string.Therefore, should the LED fail for any reason, there will still be aninterruption to operation and associated costs while the failed LED inthe series-connected string of LEDs is detected and replaced.

SUMMARY

Accordingly, one aspect of the invention provides an electronic deviceincluding a protection circuit for a light-emitting device. Theprotection circuit comprises a first node adapted to be coupled to ananode of the light-emitting device. A second node is adapted to becoupled to a cathode of the light-emitting device and a voltagedetection stage is coupled between the first and second nodes. Thevoltage detection stage is adapted to detect an overvoltage conditionbetween the first and second nodes. Furthermore, the protection circuitcomprises a thyristor (also known as a silicon controlled rectifier(SCR)) coupled with its anode to the first node, its cathode to thesecond node and to the voltage detection stage. When an overvoltagecondition is detected (e.g. in normal operation), the control gate ofthe thyristor is triggered so that current can flow through thethyristor.

When a light-emitting device in a string of series-connectedlight-emitting devices fails, the entire power supply voltage, forexample 20 V, which was dropped across the whole string of devices, isdropped across the single failed light-emitting device, leading to anovervoltage condition (an instantaneous sharp peak in the voltagedropped across the light-emitting device). If such an overvoltagecondition is detected by the voltage detection stage, the voltage at thecontrol gate of the thyristor is increased and the control gate of thethyristor receives a voltage or current pulse. This triggers or latchesthe thyristor into conduction so that it is forward biased from itsanode to its cathode. Excess current caused by the overvoltage conditionis then allowed to flow through the thyristor, thus bypassing thelight-emitting device. In other words, the failed or brokenlight-emitting device is shorted and, when the light-emitting device isseries-connected to a string of other light-emitting devices, the wholelight-emitting device string will stay in operation. This provides theadvantage that there is no interruption of operation to thelight-emitting device string and therefore no maintenance time or costis wasted. The invention also provides a means of keeping a string ofseries-connected light-emitting devices in operation without the needfor any additional complex external circuitry. This is especiallyadvantageous for products in which the light-emitting device string isrequired to have a long lifetime and low maintenance costs, and/or wheresafety is an issue, such as when the light-emitting device string isused for an application like street lighting or emergency lighting.Furthermore, with the electronic device according to the invention, itis possible to series couple many light-emitting devices together in avery long chain, rather than having multiple parallel strings oflight-emitting devices, since there is no risk of the entire chain ofdevices failing when just one device in the chain fails.

Advantageously, the device may be provided with a reporting (signal out)pin, which indicates if the thyristor is latched (fired). In this way itis possible to determine whether the thyristor is latched and thereforeif the light-emitting device is being bypassed. In this way a reportingof the condition of the device is possible.

The voltage detection stage may include a series arrangement of a diodeand a resistor coupled in parallel with the thyristor. In this case, thediode and the resistor can be connected together in series between thefirst and second nodes. The diode can be coupled with its cathode to theinput node and then a node interconnecting the anode of the diode andthe resistor can be coupled to a control gate of the thyristor. Thismeans that the diode is coupled anti-parallel to the light-emittingdevice and provides a very inexpensive solution for the voltagedetection stage, which detects an overvoltage condition when thelight-emitting device fails. Since the diode is reverse biased withrespect to the light-emitting device, when an overvoltage conditionoccurs; i.e., the voltage across the light-emitting device between theanode and the cathode is above the allowed range of operating voltagesof the light-emitting device, current is allowed to flow in the reversedirection through the diode. This causes a current or voltage pulse tothe control gate of the thyristor, which latches the thyristor andallows the current to flow through it in a direction from the first nodeto the second node (from the anode to the cathode of the thyristor),thus bypassing or short circuiting the light-emitting device.

The diode in the voltage detection stage may be implemented as Zenerdiode. If the Zener diode is chosen such that its breakdown voltage(Zener voltage) is made equal to the voltage between the anode and thecathode (the voltage across the light-emitting device) at theovervoltage condition, current will flow in the reverse direction of theZener diode when the overvoltage condition is reached. This causes thecontrol gate of the thyristor to trigger the thyristor. The current pathof the thyristor is then made conductive so that current can flowthrough the thyristor from the first node to the second node so as toshort-circuit or bypass the light-emitting device. Since current canonly bypass the light-emitting device when the voltage across thelight-emitting device exceeds the breakdown voltage of the Zener diode,the protection circuit cannot be falsely triggered. In other words, thelight-emitting device will only be short-circuited by the protectioncircuit when the overvoltage condition is reached.

In an alternative embodiment of the invention, the thyristor may beimplemented as two transistors, i.e. a PNP and an NPN bipolartransistor. The diode in the voltage detection stage may still beimplemented as Zener diode and the Zener diode may be coupled betweenthe bases of the two transistors. One or more resistors may be coupledin series to the Zener diode. The thyristor consisting of the twobipolar transistors is then made conductive if the breakdown voltage ofthe Zener diode is reached, which means that the overvoltage conditionis reached. The current path of the thyristor is then made conductive sothat current can flow through the two bipolar transistors, i.e., throughthe thyristor from the first node to the second node, so as toshort-circuit or bypass the light-emitting device.

Alternatively, the voltage detection stage may include a thermistorcoupled between the first and second nodes. The thermistor can then beadapted to provide a voltage that changes with temperature at thecontrol gate of the thyristor. The thermistor may be a resistor havingeither a positive temperature coefficient or a negative temperaturecoefficient. In the case where the thermistor has a positive temperaturecoefficient, the voltage across the resistor increases as a function ofincreasing temperature. However, the thermistor may also be implementedas a resistor having a negative temperature coefficient, which meansthat the voltage across the resistor decreases with increasingtemperature.

The voltage detection stage may also include a comparing means adaptedto receive a voltage drop across the thermistor at its input and havingits output coupled to the control gate of the thyristor. This meansthat, if the temperature of the light-emitting device should increase sothat it is outside the ambient operating range, the voltage drop acrossthe thermistor will increase or decrease (depending on whether thethermistor has a positive or a negative temperature coefficient,respectively), which causes the output of the comparing means to gohigh. Therefore, since the control gate of the thyristor is coupled tothe output of the comparing means, the control gate of the thyristor istriggered to make the thyristor conductive and current is allowed toflow through the thyristor in a direction from the first node to thesecond node, thus bypassing the light-emitting device. The device willthen be short circuited before it fails due to overheating. Thisprovides the advantage the light-emitting device may safely operate at ahigher ambient temperature, since it is automatically bypassed when itsoperating temperature increases outside the allowed temperature range.

In addition, the light-emitting device could go back to operation oncethe thermistor has cooled down to within the ambient temperature range.This functionality could be implemented, for example, by use of ahysteresis. Furthermore, the device could be provided with a signal out(reporting) pin, which could be used to determine whether the thyristoris latched (fired). This way, a reporting of the over temperature of thelight-emitting device is possible.

Advantageously, the electronic device further comprises an additionaldiode coupled in parallel with the thyristor with its anode to thesecond node and its cathode connected to the first node. In other wordsthe additional diode is coupled in an anti-parallel manner with thethyristor and the light-emitting device. This additional diode isconfigured to protect the light-emitting device from electrostaticdischarge (ESD). Therefore, in the event of an electrostatic discharge,for example up to 2 kV, current will flow in the reverse direction ofthe diode, thus short circuiting the light-emitting device andprotecting it from the overvoltage condition caused by the electrostaticdischarge.

The electronic device according to the invention may be implemented in alight-emitting device package. This light-emitting device package thenmay comprise a light-emitting device coupled to the electronic device ofthe present invention such that the anode of the light-emitting deviceis coupled to the first node and the cathode of the light-emittingdevice is coupled to the second node. In this light-emitting devicepackage, the light-emitting device may be provided on a first die andthe electronic device may be provided on a second die separate from thefirst die. Partitioning the device package so that the light-emittingdevice is provided on one die and the protection circuit in the deviceof the present invention is provided on another, separate die providesthe advantage of a device package that is very flexible and existingdesigns may be easily adapted. Furthermore, providing the protectioncircuit on a separate die from the light-emitting device means that itis possible to form device packages including the device of theinvention with any different type of light-emitting device. In addition,providing the device according to the invention on a separate die fromthe light-emitting device means that any heat generated by thelight-emitting device is not applied to the protection circuit and thusdoes not interfere with the operation of the protection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and characteristics of the invention ensue from thedescription below of the preferred embodiments, with reference to theaccompanying drawings, in which:

FIG. 1 is a simplified circuit diagram of a device package including anelectronic device with a protection circuit for a light-emitting deviceaccording to a first embodiment of the invention;

FIG. 2 is a simplified circuit diagram of a device package including anelectronic device with a protection circuit for a light-emitting deviceaccording to another embodiment of the invention;

FIG. 3 is a simplified circuit diagram of a device package including anelectronic device with a protection circuit for a light-emitting deviceaccording to another embodiment of the invention;

FIG. 4 is a more detailed circuit diagram of a device package includingan electronic device with a protection circuit for a light-emittingdevice according to another embodiment of the invention; and

FIG. 5 is a simplified circuit diagram of a device package including anelectronic device with a protection circuit for a light-emitting deviceaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a simplified circuit diagram of a device package includingan electronic device having a protection circuit for a light-emittingdevice according to a first embodiment. A device package 1 includes twodies; a first die 2 with a light-emitting device LED and a second die 3having protection circuitry provided thereon for protecting thelight-emitting device LED. The light-emitting device LED is coupledbetween an anode A and a cathode C, with its anode connected to theanode A and its cathode connected to the cathode C. The protectioncircuit provided on the separate die 3 has a Zener diode Z with itscathode coupled to the anode A and its anode coupled to a resistor R,with the resistor R also being coupled to the cathode C. The Zener diodeZ and the resistor R are connected together in series, with a nodeinterconnecting the Zener diode Z and the resistor R being connected tothe control gate CG of a thyristor T. The thyristor T is coupled betweenthe anode A and the cathode C with its anode TA to the anode A and itscathode TC to the cathode C. A diode D is connected in an anti-parallelconfiguration to the thyristor T with its cathode to the anode A and itsanode to the cathode C.

If the light-emitting device LED should fail, this causes a voltagesurge or peak; i.e., a sudden instantaneous increase in voltage, betweenthe anode A and the cathode C, in other words an overvoltage condition.The Zener diode Z is chosen so that its breakdown voltage is equal to apredetermined voltage at which an overvoltage condition occurs.

Therefore, if the voltage across the LED between the anode A and thecathode C at the overvoltage condition is greater than the breakdownvoltage of the Zener diode Z (the Zener voltage), current flows in areverse direction through the Zener diode Z from its cathode to itsanode and the voltage at the control gate of the thyristor thereforeincreases (there is a current pulse or a voltage pulse to the controlgate of the thyristor T). The control gate of the thyristor T is thentriggered to make the channel of the thyristor T conductive and thethyristor T is latched so that current flows through the thyristor T ina direction from the anode A to the cathode C, thereby short circuitingthe light-emitting device LED. This means that, in the event thelight-emitting device LED is connected in series with a string of otherlight-emitting devices, the other light-emitting devices will continueto operate since current flowing through the thyristor T bypasses theopen circuit condition of the failed light-emitting device LED. Even ifthere is no longer a voltage or current applied to the control gate ofthe thyristor T, the thyristor T will still remain conducting so as toshort circuit the LED. In other words, the thyristor T remains latchedin its ON state, even after the instantaneous voltage pulse to itscontrol gate CG caused by the overvoltage condition. As long as itsanode TA remains positively biased it cannot be switched off until theanode current falls below the holding current specified by themanufacturer. However, the thyristor T may be switched off if theexternal circuit causes its anode TA to become negatively biased.

Furthermore, in the event that there should be a voltage surge due toelectrostatic discharge (ESD), the diode D protects the LED from the ESDfor an ESD of up to 2 kV. This is because the breakdown voltage of thediode D is chosen so that when the voltage across the LED due to the ESDincreases above the breakdown voltage of the diode D, current flowsthrough the diode D in its reverse direction from its cathode to itsanode, thereby bypassing the light-emitting device LED and protecting itfrom the excess current due to the ESD.

FIG. 2 shows a simplified circuit diagram of another embodiment of theinvention. The thyristor T (silicon controlled rectifier) may beimplemented by a pair of coupled bipolar junction transistors T1 and T2.The transistor T1 is an NPN transistor and the transistor T2 is a PNPtransistor coupled with the base of T1 to the collector of T2 and thebase of T2 to the collector of T1. The emitter of T2 corresponds tothyristor anode TA shown in FIG. 1 and the emitter of T1 corresponds tothyristor cathode TA shown in FIG. 1. The Zener diode Z is coupledbetween the base terminals of T1 and T2, with a resistor R1 coupledbetween the collector terminal of T1 and the anode A and a resistor R2coupled between the collector terminal of T2 and the cathode C. Thetrigger voltage and triggered on voltage of the silicon controlledrectifier implemented by the transistors T1 and T2 can be calculatedaccording to the following. The values are given by way of example only.Trigger voltage(voltage at which the thyristor or silicon controlledrectifier is latched)=Zener voltage+V _(BE)(T1)+V _(BE)(T2),

-   -   where Zener voltage is the breakdown voltage of the Zener diode        Z, V_(BE) (T1) is the base-emitter voltage of the transistor T1        and V_(BE) (T2) is the base-emitter voltage of the transistor        T2.

For example, with a Zener voltage of 6.5 V and a base emitter voltageV_(BE) for both transistors T1 and T2 of 0.7 V,Trigger voltage=6.5 V+0.7 V+0.7 V=7.9 V, andTriggered on voltage=(Ion×R1)+V _(CE)

-   -   where Ion is the current through the thyristor arrangement when        it is latched, R1 is the resistance of the resistor R1 and        V_(CE) is the collector-emitter voltage of the transistor T1.        For example, with Ion=750 mA, R1=2Ω and 0.2 V≦V_(CE)≦0.4 V, then        Triggered on voltage=(750 mA×2Ω)+(0.2 V≦V _(CE)≦0.4 V)=1.7 V to        1.9 V.

FIG. 3 shows a further alternative embodiment of an electronic deviceimplemented in a light-emitting device package 1.

The circuit is similar to that described with reference to the firstembodiment and the same elements will be denoted with the same referencesigns. The device package 1 also comprises a light-emitting device LEDprovided on a die 2 connected between an anode A and a cathode C withits anode to the anode A and its cathode to the cathode C. However, theprotection circuit according to this embodiment has a differentconfiguration to that of the first embodiment described above and isprovided on another die 4, separate from the die 2.

In this embodiment, a thyristor T is also connected with its anode TA tothe anode A and its cathode TC to the cathode C, such that it is coupledin parallel with the light-emitting device LED when the dies 2 and 4 arecoupled. However, this embodiment differs from the first embodiment inthat the control gate CG of the thyristor T is connected to the outputof a comparator CMP. A series arrangement of resistors R3 and R4 iscoupled between the anode A and the cathode C and a node interconnectingthe resistors R3 and R4 is connected to a first input of the comparatorCMP. A series arrangement of a thermistor RT and a resistor R5 is alsoconnected between the anode A and the cathode C in parallel with theresistor arrangement R3 and R4. A node interconnecting the thermistor RTand the resistor R5 is connected to a second input of the comparatorCMP. The thermistor RT may preferably have a positive temperaturecoefficient, such that the voltage across it increases as a function ofincreasing temperature. However, alternatively, in a modified circuit athermistor having a negative temperature coefficient, such that thevoltage across it decreases as a function of increasing temperature, maybe used.

The temperature coefficient of the thermistor RT (either positive ornegative) and the resistance values of the resistors R3, R4 and R5 arechosen such that, when the LED is operating in its normal ambienttemperature range, the voltages at the first and second inputs of thecomparator CMP are equal so that the output of the comparator is low,for example. However, if the light-emitting device LED becomes too hot;i.e., its temperature increases above its ambient operating temperature,then the voltage across the thermistor RT increases (in the case whereit has a positive temperature coefficient) or decreases (in the casewhere it has a negative temperature coefficient). This means that thereis a difference between the voltages at the first and second inputs ofthe comparator CMP, which causes a voltage increase at the output of thecomparator CMP. This increases the voltage at the control gate CG of thethyristor T, which prompts the control gate of the thyristor T to openthe thyristor T so that current then flows through the thyristor T in adirection from the anode A to the cathode C. This causes thelight-emitting device LED to be bypassed or short-circuited and it isallowed to cool down. As the temperature of the LED decreases, thevoltage across the thermistor RT decreases (if the thermistor RT has apositive temperature coefficient) or increases (if the thermistor RT hasa negative temperature coefficient). Therefore, eventually the voltagesat both inputs of the comparator CMP become equal, when the LED returnsto its ambient operating temperature, and the output of the comparatorCMP is low, for example. However, the current conducting path of thethyristor T remains open and current will still flow through thethyristor T, short-circuiting the light-emitting device LED, untileither power to the thyristor T is switched off or the thyristor T isreverse biased. The LED may therefore safely operate at the upper end ofits ambient operating temperature range, since the protection circuitaccording to the present embodiment automatically allows the LED to bebypassed, should its temperature increase so as to be outside theambient operating range.

FIG. 4 shows the protection circuit of FIG. 3 provided on the die 4 inmore detail, with the thyristor T, or silicon controlled rectifier,being implemented by NPN and PNP bipolar transistors T1 and T2,respectively, as well as the resistor arrangement of R1 and R2, as shownin FIG. 2. The arrangement of resistors R3, R4, R5 and RT, and thecomparator CMP is the same as that shown in FIG. 4. The operation of thecircuit shown in FIG. 4 is the same as that described above withreference to FIG. 3.

In an alternative embodiment, the protection circuits provided on thedie 4, and shown in FIGS. 3 and 4, for short-circuiting or bypassing thelight-emitting device LED in the event that its temperature increasesabove the ambient operating range, could also be implemented with ahysteresis. In this way, once the light-emitting device LED has cooleddown again to a specific temperature within its ambient operating range,the protection circuitry can be switched off so that if the LED isoperated with pulsating DC, for example, the thyristor will turn off andthe LED will no longer be bypassed and can start operating again. Thenthe light-emitting device LED can be operated in a dedicated temperaturerange without the risk of damaging it while it is being operated at hightemperatures. In addition, if a string of light-emitting devices arebypassed at increasing temperature, less heat will be dissipated,allowing the whole system to cool down. This way, the light-emittingdevices can come back into operation one by one. Therefore the wholesystem can become more reliable in the case of an overtemperaturecondition.

FIG. 5 shows a further embodiment with a different example of anelectronic device 1 having a first die 2, on which a light-emittingdevice LED is provided, and a protection circuit provided on a seconddie 5. Again, the second die 5 is separate from the first die 2. In thiscase, a thyristor, or silicon controlled rectifier arrangement isimplemented by a PNP transistor T2 and an NPN transistor T3 having adouble emitter structure. One of the emitter terminals of the transistorT3 is coupled to a reporting pin P. The level of the emitter current Ieat the reporting pin P can then indicate the condition of the thyristor(silicon controlled rectifier); i.e., whether or not it is latched. Thebase of the transistor T2 is coupled to the collector of the transistorT3 and the base of the transistor T3 is coupled to the collector of thetransistor T2. The emitter of the transistor T2 is coupled to the anodeA and the other emitter of the transistor T3 that is not coupled to thereporting pin P is coupled to the cathode C. A resistor R1 is coupledbetween the anode A and an interconnection of the base and collector ofthe transistor T2 and the transistor T3. A resistor R2 is coupledbetween the cathode C and an interconnection of the base and collectorof the transistor T3 and the transistor T2. A diode D is coupled inparallel with the silicon controlled rectifier arrangement with itsanode to the cathode C and its cathode to the anode A.

The protection circuit provided on the second die 5 may either have avoltage detection stage implemented with a Zener diode coupled betweenthe base terminals of the transistors T2 and T3, as shown in FIG. 2, orwith the thermistor and comparator arrangement shown in FIG. 4. In bothcases, when an overvoltage condition occurs in the light-emitting deviceLED, the thyristor or silicon controlled rectifier arrangement islatched and the LED is short circuited or bypassed so that current flowsthrough the thyristor arrangement. Current Ie from the emitter of thetransistor T3 coupled to the reporting pin P then flows to the reportingpin P, which indicates that the thryristor arrangement is latched andthus that the light-emitting device LED has failed. The current Ie atthe reporting pin P can be a percentage, for example 1% or 2%, of thecurrent in the thyristor or silicon controlled rectifier arrangementwhen it is latched or fired-up. The latched or fired-up current of thethyristor can be, for example, 350 mA or 750 mA, depending on theapplication requirements of the device, as well as device layout. If thethyristor is not latched, there will be no current out of the reportingpin P, therefore this condition indicates that the LED is operationaland not being short-circuited by the protection circuitry. Informationabout the current Ie at the reporting pin can be used to generate atrue/false logic at a desired voltage level. Such a current Ie at thereporting pin P can be indicated, for example, by means of a visualindicator such as a lamp. The reporting pin P can also indicate when thetemperature of the LED has increased outside the ambient operatingrange.

Although the invention has been described hereinabove with reference tospecific embodiments, it is not limited to these embodiments and nodoubt further alternatives will occur to the skilled person that liewithin the scope of the invention as claimed.

For example, in the above-described embodiments of the presentinvention, the light-emitting device is a light-emitting diode (LED).However, this is for illustrative purposes only and the device of thepresent invention may be used in conjunction with any kind oflight-emitting device, for example a semiconductor laser. Furthermore,the protection circuits of the embodiments shown in FIGS. 2, 4 and 5 maybe used in conjunction with each other, all three embodiments together,or, alternatively, the embodiments shown in FIGS. 2 and 5 or in FIGS. 4and 5 may respectively be employed together in one protection circuit.

1. An electronic device including a protection circuit for a light-emitting device, the protection circuit comprising: a first node adapted to be coupled to an anode of the light-emitting device; a second node adapted to be coupled to a cathode of the light-emitting device; a voltage detection stage coupled between the first and second nodes, the voltage detection stage being adapted to detect an overvoltage condition between the first and second nodes; and a thyristor coupled with its anode to the first node, its cathode to the second node and to the voltage detection stage such that when the overvoltage condition is detected the thyristor is triggered to conduct so that current can flow through the thyristor, wherein the thyristor comprises a PNP transistor and an NPN transistor having a double emitter, one of the emitters of the NPN transistor being coupled to a reporting pin to indicate a condition of the thyristor.
 2. The electronic device according to claim 1, wherein the voltage detection stage includes a series arrangement of a diode and a resistor coupled in parallel with the thyristor.
 3. The electronic device according to claim 2, wherein the diode is coupled with its cathode to the first node and a node interconnecting the anode of the diode and the resistor is coupled to a control gate of the thyristor.
 4. The electronic device according to claim 2, wherein the diode is a Zener diode.
 5. The electronic device according to claim 1 wherein the voltage detection stage includes a thermistor coupled between the first and second nodes and adapted to provide a voltage that changes with temperature at a control gate of the thyristor.
 6. The electronic device according to claim 5, wherein the voltage detection stage includes a comparing means adapted to receive a voltage drop across the thermistor at its input and having its output coupled to the control gate of the thyristor.
 7. The electronic device according to claim 1, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 8. A light-emitting device including an electronic device having a protection circuit for the light-emitting device, comprising: a light-emitting device; a first node coupled to an anode of the light-emitting device; a second node coupled to a cathode of the light-emitting device; a voltage detection stage coupled between the first and second nodes, the voltage detection stage being adapted to detect an overvoltage condition between the first and second nodes; and a thyristor coupled with its anode to the first node, its cathode to the second node and to the voltage detection stage such that when the overvoltage condition is detected the thyristor is triggered to conduct so that current can flow through the thyristor, wherein the thyristor comprises a PNP transistor and an NPN transistor having a double emitter, one of the emitters of the NPN transistor being coupled to a reporting pin to indicate a condition of the thyristor.
 9. The light-emitting device package according to claim 8, wherein the light-emitting device is provided on a first die and the electronic device is provided on a second die separate from the first die.
 10. The light-emitting device according to claim 8, wherein the voltage detection stage includes a series arrangement of a diode and a resistor coupled in parallel with the thyristor.
 11. The light-emitting device according to claim 10, wherein the diode is coupled with its cathode to the first node and a node interconnecting the anode of the diode and the resistor is coupled to a control gate of the thyristor.
 12. The light-emitting device according to claim 10, wherein the diode is a Zener diode.
 13. The electronic device according to claim 2, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 14. The electronic device according to claim 3, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 15. The electronic device according to claim 4, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 16. The electronic device according to claim 5, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 17. The electronic device according to claim 6, further comprising an additional diode for protecting the light-emitting device from electrostatic discharge, the additional diode being coupled in parallel with the thyristor with its anode to the second node and its cathode to the first node.
 18. The light-emitting device according to claim 8, wherein the voltage detection stage includes a thermistor coupled between the first and second nodes and adapted to provide a voltage that changes with temperature at a control gate of the thyristor. 